Presentation on theme: "ODOT BRIDGE LOAD RATING"— Presentation transcript:
1 ODOT BRIDGE LOAD RATING GreetingI would like to discuss the next part of this course which will cover ODOT Bridge Load Rating.In the next ½ hour, I would like to discuss.-What a load rating is-Why we perform bridge load ratings-What ODOT expects in a bridge load rating submittalA basic how and why overview
2 What is a Bridge? Federal Highway Administration (FHWA) Definition: A Bridge is ANY structure that…1.) is erected over a depression or obstruction(water, highway, railway, etc.)AND2.) has a track or passageway for carrying traffic ormoving loads3.) has an opening greater than 20’-0” (measured along centerline of roadway between undercopings of abutments or spring lines of arches, or extreme ends of openings for multiple boxes; it may also include multiple pipes, where the clear distance between openings is less than half of the smaller contiguous opening)What is a Bridge?Let’s start with the first term of the phrase “Bridge Load Rating”…ON THE SIDEFHWA definition based on the National Bridge Inspection Standards published in the Code of Federal Regulations (23 CFR 650.3)FHWA: "The National Bridge Inspection Standards published in the Code of Federal Regulations (23 CFR 650.3) give the following definition: A structure including supports erected over a depression or an obstruction, such as water, highway, or railway, and having a track or passageway for carrying traffic or other moving loads, and having an opening measured along the center of the roadway of more than 20 feet* between undercopings of abutments or spring lines of arches, or extreme ends of openings for multiple boxes; it may also include multiple pipes, where the clear distance between openings is less than half of the smaller contiguous opening. * (6.1 meters)"
3 What is a Bridge? (cont.)Ohio Department of Transportation (ODOT) Definition (based on the Ohio Revised Code):A Bridge is ANY structure that…1.) is on, above, or below a highwayAND2.) Is greater than or equal to 10’-0”(measured the same way as in the FHWA definition)A 9’ diameter round pipe culvert on a skew could be considered by ODOT to be a bridge)It should be noted that these definitions include: Railroad Pedestrian, and Bikeway bridges.The differences between these definitions is important when it comes to things like…inventoryinspection &load rating……ODOT self imposes a greater range of structures than is actually required of them.ON THE SIDE:ORC: "a bridge is defined as: any structure, including supports, of 10 feet or more clear span or 10 feet or more (clear opening) in diameter on, above, or below a highway."
5 There are Two Primary Types of Loads used in Load Ratings? Permanent or Dead LoadsStructure self weightSuperimposed dead loads (barriers, overlays, utilities, etc.)Transient or Live LoadsVehicular loadsImpact loadsNext let’s look at the “Load” aspect of “Bridge Load Rating”
6 Three Types of Live Loads in Ohio Design or inventory loadsHS20-44, HS25, HL-93Ohio Legal Loads2F1, 3F1, 4F1, 5C1Permit Loads & SuperloadsDesign or inventory loads = Truck configurations developed by design codes such as AASHTOOhio Legal Loads = Truck configurations developed by ODOT that are used exclusively for load rating. The feds impose live load limitations based on a formula they call the “Federal Bridge Gross Weight Formula”. These Ohio Legal Loads are intended to cover the limits of this formula.And finally…Permit and Superloads are the extra heavy loads that require special permission to travel Ohio highways.IT SHOULD BE NOTED that the feds only require us to use highway loads for load ratings. Consequently, even though pedestrian and railroad structures fall under the definition of “Bridge”, and they are inspected and inventoried, they are not load rated.Note: The Feds only require highway loads to be used for load rating. Consequently, even though pedestrian and railroad structures fall under the definition of “Bridge”, and they are inspected and inventoried, they are not load rated
13 What Is Bridge Load Rating? The safe live load carrying capacity of a highway structure is called its load rating.It is usually expressed as a (rating) factor (RF) of a defined vehicle OR as a gross tonnage for a defined vehicle axle configurationSo, after all the dead loads are in place, we are basically asking “How much Live Load can this structure safely take?”
14 Basic Equation for Calculating the Rating Factor (RF) A load rating can be expressed in terms of a “rating factor” for a particular vehicle.How to calculate the rating factor (RF)A1 = Factor for dead loadsA2 = Factor for live loadC = Capacity of the bridgeD = Dead load effectI = Impact factorL = Live load effectC – A1 * DThe factors A1 and A2 depend on which Method and Type of Load rating you are doing.RF =A2 * L*(1 + I)
15 Three Different Load Rating Methods Allowable Stress (ASD)Also known as Working Stress (WSD)Used for ODOT steel trusses and timber structuresLoad Factor (LFD)ODOT PreferredFHWA PreferredLoad & Resistance Factor Rating (LRFR)NCHRP Project 12-46Currently, 95% of all ODOT bridges have been load rated using the LFD method.Although the feds are requiring LRFD for design in 2007, ODOT is still planning to require that all load ratings be done using the load factor method. I am told that the feds are still going to REQUIRE Load Factor load ratings for the next 4-6 years.
16 Two Types of Ohio Load Ratings Inventory Rating (Design Level)1.) HS20-44Operating Rating (Service Level)2.) HS20-443.) 2F14.) 3F15.) 4F16.) 5C1There are TWO types of load ratingsInventory &Operating RatingsThe A1 and A2 factors used for Inventory ratings are based on a design levelThe A1 and A2 factors used for Operating ratings are more based more on an in service condition.Every bridge in Ohio has six different load rating factors calculated.
17 Factors for LFD Load Rating Ref: AASHTO Manual for Condition Evaluation of Bridges 2000
18 What components of a bridge is ODOT interested in Load Rating All primary superstructure components of a bridge shall be load rated.Unless specified in a scope, this excludes the following:Decks (unless bridge is a deck slab type)BearingsSubstructuresField splicesRailing / Parapets
19 When Should a Load Rating be Revised? The load rating of a bridge should be revisedwhen:there is a change in the dead load on the structurethere is a physical change in any structural member of the bridge.there is a change in the proposed live loadingA different method of analysis is requiredExamples of #1addition or removal ofwearing surfacesSidewalksParapetsRailingsUtilitiesExamples of #2when there is an alteration in the structurewhen a new beam or a girder is placedwhen a new deck is addedwhen there is rusting or damage to a beam, girder or other structural element that has resulted in section losswhen there is structural damage to the bridge members due to accidents (i.e. a vehicular collision)when excessive deflection or elongation is observed under temperature or highway loadswhen there is excessive structural damage (i.e. spalling or salt related damage to concrete)Examples of #3:Permit loadsSuperloadsExample of #4:When codes change (i.e. ASD to LFD and then eventually to LRFR)
21 Why do we rate structures? (1) The Silver Bridge CollapseThe Dec. 15, 1967, collapse of the Silver Bridge at Point Pleasant, Ohio killed 46 people. The failure of the 39 year old eye bar suspension bridge across the Ohio River prompted US Congress to pass National Bridge Inspection Standards (NBIS) in 1968.This collapse prompted the feds to require ORGANIZED inspection departments.It was at this time that ODOT established their Inspection and Load Rating DepartmentsSince the collapse occurred in Ohio, the state felt obligated to stay ahead of these newly established fed requirements…1.) while the feds required inspections every 2 years, ODOT established annual inspection requirements2.) while the feds defined a bridge starting at 20’ in length, ODOT defined bridges starting at 10’
22 Why do we rate structures? (2) Required by Federal government (NBIS)To monitor safety of structures over timeTo help determine when rehabilitation or replacement is needed
23 Why do we rate structures? (3) To determine if a bridge needs to be posted for a load restriction as required by the Ohio Revised CodeTo have a consistent summary of load carrying capacities of all state bridgesTo assist Office of Permits in their processing of Permit and SuperloadsTab #1: Actually, the OHIO Revised Code (ORC), Section doesn’t specifically require load rating. It requires us to post warning signs when a structures capacity drops below a specified threshold. But it is the load rating analysis gives us the needed information to comply with the posting requirement.Tab #2: Different design vehicles have been used in the past for the design of bridges ( e.g., H-15, HS20, HS25, etc.). Some bridges have aged, deteriorated or become structurally deficient during the course of their life. To have a consistent summary of the load carrying capacities of all the bridges in the state of Ohio, all bridges are rated using a standard set of vehicles, called Ohio Legal Loads.Tab #3: ODOT has an internal need to load rate structures for the purpose of assisting the Office of Permits in their processing of Superload (vehicles > 120 kips) permits. The Office of Structural Engineering will check all structures along the desired Superload route against the proposed vehicle loading configuration. They will utilize batch routines to re-run already generated models where possible.
25 A Permit* load equals…any vehicle or combination of loads having a gross weight in excess of 40 tons (or 80 kips).The 40 tons limit was established, because it is the maximum gross weight of the four Ohio Legal Loads (5C1 truck).* = Permits are also required for over-SIZED vehicles. But, for the purposes of load rating, we are referring to permits that are required due to over-weight only.
26 A Superload equals…any vehicle or combination of loads having a gross weight in excess of 60 tons (or 120 kips).The top picture is from Diamond Heavy Hauling company. The transporter is about 205' long and weighs about 200,000 pounds. It is manufactured in Shandon, Ohio.The bottom picture was from a gas turbine transport in The gross weight is 673 kips.
27 Vehicle Categories based on weight 1.50 * 40NO PERMIT REQUIRED (<= 40 tons)You and me driving our cars on the bridgePERMIT LOAD VEHICLES (40 tons <weight <= 60 tons)- 60 ton limit is based on 150% times 40 tons (the gross weight of the heaviest Ohio Legal Load, 5C1)SUPERLOAD VEHICLESGross weight of heaviest Ohio Legal Load (5C1)
29 Of those permits issued, how many are for Superload vehicles?
30 How many Superload routes does the OSE check each year? You can see from this chart that the trucks traveling our highways are getting heavier and heavier.This clearly illustrates the importance of knowing the live load limits of each bridge on the inventory.It is also easy to see that there is a need for tools that allow engineers to quickly load rate structures.
31 Computer programs to assist in load rating ODOT bridges AASHTO BARS-PC (SHALL be used where possible)(BRASS (SHALL be used for buried structures)(BARS (REQUIRED WHERE POSSIBLE)Steel beams/girdersPrestressed and Reinforced Concrete beams/girdersConcrete DecksSteel TrussesBRASSCast-in-place or precast box or frame type buried structures (2’-0” or more of fill on top)
32 Additional Computer programs to assist in load rating ODOT bridges DESCUS I (STAAD III/Pro (GT STRUDL (Finite Element based)(SAP 90 / SAP 2000 (Finite Element based)(DESCUSCurved Steel beams/girdersSTAADFairly comprehensive general analysis program. Can do most anything (steel, concrete,prestressed, post tensioned, trusses, etc.)GT STRUDL and SAP 2000Finite element analyses.
33 Why is BARS desirable to ODOT? Can run Batch routines (useful for fast analysis of superload routes)Fast, free, and doesn’t require a lot of resourcesTested and used over the last 20+ yearsProvides output in rating formatSupports both Mainframe and PC computersCustom vehicles can be easily definedUseful for reviewing new designs
34 BARS on the InternetThe program and instruction manuals can be downloaded for free at…An introductory tutorial can be downloaded at…(An AASHTOWARE Product)
37 BDM Section 900 (1) BURIED STRUCTURES ALL bridges (> 10’) with fill > 2’-0” shall be considered “buried” and shall be load ratedEXCLUDING…Circular Steel pipesCircular Plastic pipesCircular Concrete pipesBuried Metal BoxesBuried Metal FramesJunction ChambersManholesInlets
38 BDM Section 900 (2) BURIED STRUCTURES (cont.) All buried structures that are a part of new construction, replacement, or rehabilitation projects shall be load rated as follows…CIP Concrete bridges shall be load rated by the designer using BRASS-Culvert.Precast concrete frames, arches, Conspans, and Bebo type structures shall be load rated by the manufacturer.Precast boxes will be load rated by OSE using BRASS-Culvert.
39 BDM Section 900 (3) NON-BURIED STRUCTURES ALL bridges (> 10’) with fill < 2’-0” (or no fill at all) shall be considered “non-buried” and shall be load ratedBARS-PC SHALL BE USED when possibleBRASS-Culvert SHALL BE USED for concrete boxes and three-sided culvertsOSE MUST be contacted if any other software is going to be used
40 BDM Section 900 (4) MISCELLANEOUS INFORMATION Only load rate spans or portions of buried structure that will experience live loadLoad ratings of new or rehabilitation bridge projects shall be based on final design plans and shall show results that meet or exceed the design loadingNo FWS shall be included in load ratingsTAB #2: Even though the load rating uses an HS20 vehicle, the rating in gross tons for a new project should have results of HS25 or greater since HS25 is now being used as the design load.
41 BDM Section 900 (5) WHEN DO YOU SUBMIT YOUR ANALYSIS? MAJOR OR MINOR PLAN DEVELOPMENT(OR DESIGN BUILD) PROCESSInclude load rating report with STAGE 2 submittal **MINIMAL PLAN DEVELOPMENTInclude load rating report with STAGE 3 submittal ****Revise and resubmit load rating to District ProjectManager if design plans change after Stage 2(or Stage 3) and prior to contract sale
42 BDM Section 900 (7) WHEN DO YOU SUBMIT YOUR ANALYSIS? VALUE ENGINEERING CHANGE PROPOSAL (VECP)Include load rating analysis with the Final VECP submission to the District Construction Engineer
43 BDM Section 900 (8) WHAT DO YOU PUT IN THE REPORT? A full project descriptionPrintouts of analysis software input/outputExplanation of how material properties were determined (for existing structures)All hand calculationsA table summarizing the following rating factors for each live load truck…Inventory & Operating ratings for each main bridge member analyzed (Beam 1, Beam 2, Interior, Exterior, etc.)Overall ratings of each structure unit (mainline,ramps, etc.)Overall ratings of entire bridgeFull Project Description would include:PID#Bridge #SFNBridge DescriptionMethods usedAssumptions madeAll ratings shall be expressed in terms of specific truck tonnages and rounded to the nearest single digit decimal pointi.e… RF*20 for HS orRF*(gross vehicle weight in tons for Legal loads)
44 BDM Section 900 (9) WHAT DO YOU PUT IN THE REPORT? 36*1.38 = 49.8 LoadingGross VehicleWeight(Tons)RatingFactorMemberLocationInventoryHS-20-44361.3849.8 tons(HS27.7)Girder 2MidspanOperating2.3183 tons(HS46.1)Ohio LegalLoads (%)-3.08308%2F1154.8773.1 tons3F1233.4178.4 tons4F1273.0983.5 tons5C140123.3 tons20*1.38=27.7(Mouse click to get circles)You will notice that even though the gross weight of an HS20 truck is 36 tons the HS rating is 20*1.38 or HS27.7The Inventory rating in this example is 49.8 tons which is equal to the 1.38 rating factor * 36 tons.The 308% summary rating for the Ohio Legal Loads is equal to the smallest rating factor of all four legal loads times 100.Smallest * 100= 308
45 BDM Section 900 (11) WHAT DO YOU SUBMIT TO ODOT? 2 - Printed copies of load rating report(signed and sealed by an Ohio PE)1 - Electronic copy of load rating report1 – Electronic copy of input data filesBARS -LISTA.LIS, RATE2.LIS, SUMMARY.LIS,and FLEX.LIS filesBRASS -Files with the following extensions:DAT, CUS, and XMLElectronic copy can be either a CD or an attachment
46 AASHTO Load Rating References AASHTO (2002), Standard Specifications forHighway Bridges, 17th ed.,AASHTO (2000), Manual for ConditionEvaluation of Bridges, 2nd Edition. (Section 6)AASHTO (1995), Bridge Analysis and RatingSystem, BARS-PC, Release 5.5, Mod 3.3,Users Manuals I and II,
68 Live load distribution factor AASHTO Standard Specification for Highway Bridges 2002CASE B – Main Reinforcement Parallel to TrafficS = Effective Span length in feet(AASHTO )For wheel loads, the distribution widthE = *S 7’S = 16+1 = 17 feetE = *17 = 5.02 feetBARS Dist. = 1/5.02= 0.199
69 Impact load (Impact factor) AASHTO Standard Specification for Highway Bridges 20023.8.2 Impact FormulaThe amount of impact allowance, I, as a fraction of the live loadI = 50 / (L + 125) 0.3L = Effective Span length in feetI = 50 / ( ) = 0.352Use I = 0.3
70 Superimposed Dead Load ((3” / 12)* 1 ft* 145 pcf) + ((3/4” /12) * 1 ft * 120 pcf) +12 plf guardrail = lb/ftRebar distance to top of slab(11.5”–1” clear due to delamination- 5/8”–(7/8”) / 2 ) =9.4375”
71 Interactive Bridge Data Entry AA NEW XDMH - B&N *LF* POSTSPECSPEC 17.0DMH - B&NBSEN LFSEN OVER BRANCH OF WOLF CREEK, SFN:SINGLE SPAN CONCRETE SLAB BUILT IN 1926, 16 FOOT CLEAR SPAN" ASPHALT W.S. (DATE: N/A) ON 0.75" OF SOIL, 40.5' SLAB WIDTHS RCS WSS